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material for these purposes, varieties being selected which require 

 an unnecessary amount of tinne and care to shape ; and which, 

 after an exposure of a season or two to the atmosphere, assume 

 a rusty tint, in consequence of containing too large a quantity of 

 oxide of iron. To avoid the former of these defects, it is only 

 requisite to examine closely the form and texture of the freshly 

 fractured surfaces of the rock, which should generally split with 

 a smooth, even, somewhat conchoidal fracture, and present to 

 the eye a very regular and close grain, with a clear, uniform, 

 and decided tint, either of gray, or grayish-blue, or blue. To 

 detect the presence of an injurious proportion of the oxide of 

 iron, calculated in course of time to stain the exposed surface of 

 the rock, one of the readiest and simplest methods is to reduce a 

 portion to powder, moisten it with a little water, and add a little 

 pure muriatic acid. The existence of oxide of iron will be 

 made apparent by a brownish tinge, seen while the material is 

 dissolving. 



{b.) Another highly useful purpose to which this rock is often 

 applied, is in the construction of McAdam roads. As a road- 

 stone, to be employed where the intercourse does not require a 

 very heavy draught, it is at once the cheapest, most readily pro- 

 cured, and easily broken material accessible to very exten- 

 sive and important districts, not merely of New Jersey, but of 

 the Middle States. Much judgment, it is believed, may be dis- 

 played in the selection of those kinds which will prove the toughest 

 and most ditlicult to abrade under the wheels. Those possessing 

 a subcrystalline texture, and a rough, irregular fracture, espe- 

 cially when they contain a certain amount of silica and oxide of 

 iron, I have usually conceived to be the best adapted to endure at- 

 trition. A little practice with the hammer, will soon enable us to 

 ascertain approximately, the kinds likely to prove most suitable. 



(c.) Marbles. — The great calcareous formation which we have 

 described, is characterized by several varieties which are fairly 

 entitled to the name of ornamental marbles, when we consider 

 their fineness of grain and susceptibility of a delicate polish, com- 

 bined with their several soft and pleasing shades of colour. 



Among the beds which pass ordinarily by the name of lime- 

 stone, we meet with portions uniting the requisites of texture with 

 the most beautiful and delicate tints ; some are of a very pale- 



